In the market, many coffee makers claiming to have both milling and brewing functions simply pack a motorized coffee mill and a regular coffee maker together under one roof. Coffee beans are being milled and brewed in separated chambers. Some coffee makers do provide a built-in channel to transfer milled coffee powder from the milling chamber to the brewing chamber. However, the channel connecting the two chambers is hidden and is not accessible to be cleaned, which creates a hygiene issue.
The coffee maker of the type described above is disclosed in U.S. Pat. No. 4,962,693. In the coffee maker, a chopping blade and a brewing basket are mounted together to provide milling and brewing in one chamber. The chopping blade is driven by a motor all the time, while the brewing basket is driven by the chopping blade, which depends on a clutch mechanism. The clutch mechanism has a coil spring which engages or disengages the brewing basket from the chopping blade depending on the rotational direction of motor.
The clutch design is complicated and ends up the accumulated mechanical tolerance which creates misalignment between the brewing basket, chopping blade and motor. As such, when the brewing basket is rotated at a high speed, an intense oscillation and a big noise will be generated.
Using this coffee maker, hot water must be added to the coffee powder before the motor starts to wet all coffee powder thoroughly, in order to provide an even load distribution inside the brewing basket to end up less vibration and noise during brewing. However, the timing to wet all coffee powder varies with many uncontrollable factors, such as the amount of powder, size of powder, nature of the coffee. If the timing is too short, a mixture of un-wetted and wetted coffee powder lumps is generated, which creates an uneven load distribution. If the timing is too long, the hot water stays with the coffee powder for long time, which makes the coffee bitter.
Using this coffee maker, centrifugal force drives the permeated coffee powder to the top of the brewing basket where a filter paper is installed. Brewed coffee is filtered out through the filter paper and falls into a collector tray outside the basket. The filtration area is small and is not effective for filtering. When the speed of filtration of brewed coffee is slower than the speed of feeding the hot water, the hot water stays with the coffee powder before being filtered out. Consequently, there is a potential problem of overflow.